Keyboards are indispensable computer hardware for data and command input. Moreover, as the function of the computer becomes more diverse and powerful, the keyboard is provided extra function keys or hot keys for multimedia functions such as play, forward, rewind, volume up, volume down, e-mail and Internet . . . etc.
The above-mentioned functions are generally achieved by adding a prefix “E0” to the standard keycode of the keyboard to extend the function of the keyboard. However, this kind of keyboard uses exclusively the PS/2 interface.
Moreover, USB (Universal Serial Bus) is also a popular serial interface for keyboard and mouse with hot plug feature. Therefore, user can conveniently change peripherals with USB interface.
However, the keyboard with USB interface has limitation on certain function because of the definition of USB specification. For example, hot keys of some keyboards have two keycode pages selected by driver program, but the USB keyboard cannot select one keycode page from the two keycode pages. Therefore, the USB keyboard cannot be switched to vender defined page once the driver program is activated.
As can be seen from above description, the USB keyboard lacks of some function provided by the PS/2 keyboard, which is inconvenient to the user.